| 1 |
A 3-phase induction machine has a 4-pole, star-connected stator winding and runs on 400 volts, 50 Hz supply. The rotor resistance is 0.1 Q and reactance is 0.9 2. The stator-to-rotor turns ratio is 1.75 and the rated slip is 5%. The value of maximum torque and the corresponding speed will be
- 184.79 N-m; 1533.5 rpm
- 184.79 N-m; 1333.5 rpm
- 18.794 N-m; 1333.5 rpm
- 18.479 N-m; 1533.5 rpm
|
| 2 |
The maximum efficiency of 100 kVA, the single-phase transformer is 98% and occurs at 80% of full load 0.8 of lag. If the leakage impedance of the transformer is 6%, then voltage regulation at a rated load of 0.8 pf lead will be placed). |
| 3 |
Two 440/220 volts transformers are operated in parallel to share a load of 125 kVA at 0.8 pf lagging, the transformers are rated as
- A: 100 kVA; 0.8% resistance and 6% reactance
- B: 50 kVA; 1.0% resistance and 5% reactance
Find the active power load carried by transformer B. (Round off to 2-decimal digits in kW) |
| 4 |
A 230-volt shunt motor has R₁ = 0.4 2 and R₁ = 115 2. Motor takes 20 A while driving constant torque load at 800 rpm. If speed needs to be increased to 1000 rpm by d weakening by increasing resistance in the field circuit, then find the value of extra distance to be inserted in the field circuit is be a straight line). (Round off up to two decimal digits) |
| 5 |
A 400 volts, 3-phase star-connected synchronous motor with X₁ = 6 2 and X₁ = 4 2, is running in parallel with an infinite bus. If its field current is reduced to zero, then which of the following is correct?
- The maximum load that can be put on a synchronous motor is 6.66 kW.
- Armature current corresponding to maximum power is 50 A.
- The power factor at maximum power is 0.1958 leading.
- The power factor at maximum power is 0.1958 lagging.
|
| 6 |
A 2200-volt, 3-phase star-connected synchronous motor is connected to an infinite bus- bar at rated voltage. The synchronous impedance is (1 + j10) 2 per phase. If the excitation voltage is adjusted to 2800 volts for an input power of 300 kW, then the load angle will be a degree. (Round off up to two decimal digits) |
| 7 |
A 230/115 volts, 52.9 kVA, 50 Hz single phase transformer has the following parameters.
R₁ = 0.08 Ω
Χ₁ = 0.32 Ω
R2 = 0.02 Ω
Χ2 = 0.06 Ω
Total core loss = 4.232 kW
If the transformer is operating at full load 0.8 p.f lag, then which of the following is correct?
- The p.u resistance of the transformer is 0.16 p.u.
- For an input voltage of 230 volts, its secondary terminal voltage across the load will be 123.28 volts.
- Efficiency of the transformer at 3/4th of full load 0.8 pf lag is 86%.
- Maximum efficiency of the transformer occurs at a loading of 70.71%
|
| 8 |
A DC generator has 8-pole, 480 armature conductors, and is wave wound. If the generator supplies a current of 100 A and the brushes are shifted by 5º mechanical, then the demagnetizing armature reaction will be ces). AT/pole. (Round off up to two decimal |
| 9 |
The stator of a 3-phase, 4-pole ac machine has 72 slots. The stator is wound with double-layer winding and winding is short-pitched by 3-slots. Find the number of slots having top and bottom layers belonging to different phases. |
| 10 |
A 3-4 delta-connected synchronous generator is rated 100 M.W., 0.8 p.f lagging, 13.6 kV, 50 Hz, 100 rpm. If the generator's full load efficiency is 97% (neglecting field copper ss), then the prime-mover of the alternator will have an output torque of kN-m. (Round to two decimal digits) |
| 11 |
A 250 volts de series motor has an armature resistance of 1 2 and field winding resistance of 0.4 Ω. The motor takes 20 A when rotating a certain load. If the load torque varies as a cube of speed, then the value of extra resistance required in series to reduce the speed of the motor to 70% of the previous value is to be unsaturated. (Round off 2 decimal digits) Ω. Assume magnetic circuit |
| 12 |
A 3-0, 50 Hz, 4-pole, 50 kW, 440 volts star connected induction motor takes 3 kW under no-load conditions. When a block rotor test is conducted on it at 0.03 pu voltage it takes 4 kW of input power. Assuming its stator and rotor copper losses are equal under rated load conditions and rotational losses are 30% of no-load loss, then the full load slip of the motor will be put. [Neglect stator & Rotor Cu loss during no-load condition]
- 0.0378
- 0.383
- 0.0783
- 0.046
|
| 13 |
A 3-phase, 8-pole induction motor has frequencies of stator and rotor emf as 40 Hz and 2.5 Hz respectively. The motor speed is rev/sec. (Round off up to 2 decimals) |
| 14 |
A 3-phase, 6-pole, 1000 rpm, star-connected cylindrical rotor-type generator has 180 slots in the armature. The value of the distribution factor for the 7th order harmonic component of generated voltage is (Round off to two decimal places) |
| 15 |
When a single-phase transformer is connected to a 240 V, 50 Hz supply, the core loss is 600 W. When the supply is reduced to 192 V, 40 Hz, the core loss is 400 W. The value of hysteresis loss in the transformer for 240 V, 50 Hz supply will be off up to 2 decimals) watts. (Round |
POST YOUR COMMENT